The present invention relates to transmission systems for transmitting analog data on an unshielded twisted pair (UTP) of wires. More specifically, this invention is directed to an integrated gigabit Ethernet transmitter.
The past few years has witnessed an almost exponential growth in the extent of high speed data networks, and the data transmission speeds contemplated over such networks. In particular, bidirectional data transmission in accordance with the various Ethernet network protocols, over unshielded twisted pair (UTP) wiring, has emerged as the network implementation of choice for general commercial LAN installations as well as for some of the more prosaic residential and academic applications.
Local Area Networks (LAN) provide network connectivity for personal computers, workstations and servers. Ethernet, in its original 10 BASE-T form, remains the dominant network technology for LANs. However, among the high speed LAN technologies available today, Fast Ethernet, or 100 BASE-T, has become the leading choice. Fast Ethernet technology provides a smooth, non-disruptive evolution from the 10 megabits per second (Mbps) performance of the 10 BASE-T to the 100 Mbps performance of the 100 BASE-T. The growing use of 100 BASE-T connections to servers and desktops is creating a definite need for an even higher speed network technology at the backbone and server level.
The most appropriate solution to this need, now in development, is Gigabit Ethernet. Gigabit Ethernet will provide 1 gigabit per second (Gbps) bandwidth with the simplicity of Ethernet at lower cost than other technologies of comparable speed, and will offer a smooth upgrade path for current Ethernet installations. With increased speed of Gigabit Ethernet data transmission, it is evident that EMI emission and line reflections will cause the transmitted signal to become substantially impaired in the absence of some methodology for filtering the transmitted data.
Therefore, there is a need for an integrated transmitter in a data transmission system for pulse shaping digital input data and reducing EMI emissions, implemented with relatively simple circuitry.
The aforementioned need in the art for an integrated transmitter is addressed by a transmitter that is power efficient and has reduced electromagnetic interference (EMI) emissions for unshielded twisted pair (UTP) data communication applications. Transmit data is processed by a digital filter. The digital filter is integrated with a DAC binary decoder in a memory device such as a read-only memory (ROM) with time multiplexed output. The digital filter output data is converted to a current-mode analog waveform by a digital-to-analog converter (DAC). DAC line driver cells are adaptively configurable to operate in either a class-A or a class-B mode depending on the desired operational modality. A discrete-time analog filter is integrated with the DAC line driver to provide additional EMI emissions suppression. An adaptive electronic transmission signal cancellation circuit separates transmit data from receive data in a bidirectional communication system operating in full duplex mode. For a multi-transmitter system, timing circuitry staggers the time base of each transmitter to reduce the aggregate EMI emissions of the multi-transmitter system.